The VOP_GETPAGES() method is
called to read in pages of virtual memory which are backed by
ordinary files. If other adjacent pages are backed by adjacent
regions of the same file, VOP_GETPAGES() is requested to
read those pages as well, although it is not required to do so. The
VOP_PUTPAGES() method does the converse; that is to say, it
writes out adjacent dirty pages of virtual memory.

On entry, the vnode lock
is held but neither the page queue nor VM object locks are held.
Both methods return in the same state on both success and error
returns.

The arguments are:

vp

The file to access.

m

Pointer to the first
element of an array of contiguous pages representing a contiguous
region of the file to be read or written.

count

The number of pages in
the array.

sync

VM_PAGER_PUT_SYNC if
the write should be synchronous.

rtvals

An array of VM system
result codes indicating the status of each page written by
VOP_PUTPAGES().

reqpage

The index in the page
array of the requested page; i.e., the one page which the
implementation of this method must handle.

offset

Offset in the file at
which the mapped pages begin.

The status of the
VOP_PUTPAGES() method is returned on a page-by-page basis in
the array rtvals[]. The possible status values are as
follows:

VM_PAGER_OK

The page was
successfully written. The implementation must call
vm_page_undirty(9) to mark the page as clean.

VM_PAGER_PEND

The page was scheduled
to be written asynchronously. When the write completes, the
completion callback should call vm_object_pip_wakeup(9) and
vm_page_io_finish(9) to clear the busy flag and awaken any other
threads waiting for this page, in addition to calling
vm_page_undirty(9).

VM_PAGER_BAD

The page was entirely
beyond the end of the backing file. This condition should not be
possible if the vnode’s file system is correctly
implemented.

VM_PAGER_ERROR

The page could not be
written because of an error on the underlying storage medium or
protocol.

VM_PAGER_FAIL

Treated identically to
VM_PAGER_ERROR

VM_PAGER_AGAIN

The page was not
handled by this request.

The
VOP_GETPAGES() method is expected to release any pages in
m that it does not successfully handle, by calling
vm_page_free(9). When it succeeds, VOP_GETPAGES() must set
the valid bits appropriately, clear the dirty bit (using
vm_page_undirty(9)), either activate the page (if its wanted bit is
set) or deactivate it (otherwise), and finally call
vm_page_wakeup(9) to arouse any threads currently waiting for the
page to be faulted in, for each page read.

RETURN VALUES

If it successfully reads
m[reqpage], VOP_GETPAGES() returns VM_PAGER_OK;
otherwise, VM_PAGER_ERROR. By convention, the return value of
VOP_PUTPAGES() is rtvals[0].